There is a rapidly developing market for pure butene-1 for use as a monomer in the production of polybutylene. At the present time the commercial production of butene-1 requires isolation of a C.sub.4 stream containing a relatively high concentration of the 1-isomer, for example, the product of steam cracking, followed by separation of butadiene by extractive distillation, extraction of isobutylene with dilute sulfuric acid and finally distillation. Other commercial methods include molecular sieve absorption of the linear olefins (efficiently used with low concentrations of n-butenes) and selective reaction of isobutylene to methyl-tertiary butyl ether (MTBE) followed by distillation of the unreacted olefins.
Isomerization of butene-2 to butene 1 has not normally been used because the equilibrium concentration of butene-1 in the mixture at reasonable temperatures is too low to allow economic separation by distillation. It has been known for some time that olefins can be isomerized under mild conditions using a catalyst of palladium oxide supported on alumina in the presence of hydrogen. The actual active catalyst is probably palladium hydride which is produced during operation. Sufficient hydrogen must be fed to maintain the catalyst in the active form because hydrogen is lost from the catalyst by hydrogenation or slow evolution from the hydride.
As commercialized, hydroisomerization is a process used to upgrade C.sub.4 streams, usually from fluid catalytic cracking units. In the fixed bed process as practiced by some, butadiene contaminating the feed is hydrogenated to butenes, and the butenes are isomerized to the equilibrium mixture which is predominately butene-2. The advantage of that process is to remove butadiene which causes the loss of acid used in the alkylation process and improvement of the alkylate octane number in HF alkylation by using mostly butene-2 in the feed rather than butene-1.
Palladium catalysts are known and used for the butene-1 to butene-2 isomerization, As a matter of fact, because of its activity, one source, IFP, does not recommend palladium for use in streams where butene-1 is to be recovered.
According to the literature, isomerization occurs only after hydrogenation of the butadiene. In the fixed bed processes a three to four percent relative loss of butene occurs due to hydrogenation as the isomerization is pushed toward equilibrium.
The use of catalytic distillation processes is known in the art. See for example the series of patents assigned to Chemical Research and Licensing Company including U.S. Pat. Nos. 4,215,011;4,232,177; 4,242,530; 8,302,356; 4,307,254; 4,336,407; 4,439,350; 4,443,559; 4,482,775; 4,504,687; 4,510,336; and 4,536,373. Catalytic distillation has been used in the isomerization of C.sub.4 alkenes as noted in U.S. Pat. No. 4,482,775 listed above. However such a process used an acidic cationic exchange resin catalyst to produce iso and normal butenes.
The advantage sought to be achieved is relatively higher production levels of butene-1 which can be used as the monomer for polybutylene production. Another benefit would be to convert butadiene to butenes.